(1) Field of the Invention
The present invention relates to an image forming apparatus, such as a digital color copying machine and a color facsimile machine, which reproduces a full-color image according to image data obtained by performing color-separation on an original image.
(2) Related Art
In a copying machine which reproduces an image according to image data obtained by reading an original with a scanner, the digital image data of red (R), green (G), and blue (B) obtained from an original, are transformed into data of cyan (C), magenta (M), and yellow (Y) used for color image reproduction.
During the data processing, however, image noise is caused by low scanning accuracy, poor color reproducibility of the printer, and other factors, and that is why a correction unit is necessary for an image forming machine to perform corrections.
When reproducing a full-color image, smoothness is required in uniform density regions, and the presence of even a small amount of noise is likely to catch the user's attention and thus ruin their overall impression of the image.
In the prior art, to avoid such image deterioration, image noise is reduced by performing smoothing with filters on the image data of each primary color read from the original.
In the above noise reducing method, however, there are problems that necessary image data are lost during the image processing, while noticeable noise still remains on the reproduction image due to the insufficient noise removal.
These problems arise because the conventional noise removal is performed not on the actual reproduction colors recognizable to the eye, but on the image data of primary colors R, G, and B prior to color reproduction. According to prior art, desirable effects of noise removal can be rarely obtained by smoothing, because subtle image data which need to be reproduced are lost due to unnecessary smoothing, and also because image noise small enough to be ignored at the stage of processing the image data of R, G, and B may become unfavorably large as a result of the overlap of all primary colors during color reproduction.